BUSINESS SEGMENTS - Financial Information for Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Interest income	$ 310	$ 273
Interest expense	79	47
Net Interest Income	231	226
Provision for credit losses	14	14
Non-interest income	65	67
Non-interest expense	162	167
Amortization of intangibles	4	4
Income tax expense (benefit)	22	21
Net income (loss)	94	87
Total assets	33,695	31,652	$ 33,102
Total intangibles	2,330	2,339
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	310	264
Interest expense	76	42
Net Interest Income	234	222
Provision for credit losses	14	12
Non-interest income	51	53
Non-interest expense	147	149
Amortization of intangibles	4	4
Income tax expense (benefit)	23	22
Net income (loss)	97	88
Total assets	33,598	31,424
Total intangibles	2,301	2,315
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Interest income	0	0
Interest expense	0	0
Net Interest Income	0	0
Provision for credit losses	0	0
Non-interest income	11	11
Non-interest expense	9	8
Amortization of intangibles	0	0
Income tax expense (benefit)	0	1
Net income (loss)	2	2
Total assets	27	25
Total intangibles	10	10
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	0	0
Interest expense	0	0
Net Interest Income	0	0
Provision for credit losses	0	0
Non-interest income	5	4
Non-interest expense	4	4
Amortization of intangibles	0	0
Income tax expense (benefit)	0	0
Net income (loss)	1	0
Total assets	25	20
Total intangibles	19	12
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	0	9
Interest expense	0	1
Net Interest Income	0	8
Provision for credit losses	0	2
Non-interest income	0	1
Non-interest expense	0	5
Amortization of intangibles	0	0
Income tax expense (benefit)	0	0
Net income (loss)	0	2
Total assets	0	170
Total intangibles	0	2
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	0	0
Interest expense	3	4
Net Interest Income	(3)	(4)
Provision for credit losses	0	0
Non-interest income	(2)	(2)
Non-interest expense	2	1
Amortization of intangibles	0	0
Income tax expense (benefit)	(1)	(2)
Net income (loss)	(6)	(5)
Total assets	45	13
Total intangibles	$ 0	$ 0